Surely there are any number of things Spock could have done when faced with the two Kirks. For instance, he could have stunned both of them and then had a hundred security personnel beam down from the ship to deal with the problem while he sorted Garth and Kirk out at his leisure.

Garth has an explosive so powerful that one flask of it can vaporize an entire planet? Hardly seems likely, that's far more powerful than even an antimatter reaction. Still, the drop used on Marta doesn't do much and Garth is insane after all, so maybe he's just delusional.

Body Count :

Marta is blown up by Garth.

Factoid :

This episode establishes that the Federation has only fifteen incurably insane people in its entire population - and those are cured at the end of the episode!

The episode title is from Euripedes, who said "Whom the gods would destroy they first make mad."

Plotline

The Enterprise visits the Elba 2 asylum colony, repository of the few remaining criminally insane Federation citizens - including Captain Garth, a former Starship captain and hero of Kirk's who was sent to the colony after attempting to wipe out a civilisation on one of his missions. The ship is bearing a new medicine which is capable of curing all such cases of insanity.

On beaming down Kirk finds that Garth has used a unique shape-shifting ability taught to him by the inhabitants of the planet Antos to take over the the asylum. Garth plans to impersonate Kirk and beam up to the Enterprise to take control of the ship.

After Garth arouses Spock's suspicions when he fails to give the correct password for beam-up, the First Officer beams down and finds Kirk facing his identical double. The Captain manages to win out in a fight with Garth, and the Elba 2 colony is returned to the control of Dr. Cory, it's supervisor. Afterwards the new drug is supplied to the inmates and the Federation's last criminally insane citizens are cured.

Analysis

I'm not a great fan of this episode; it's too similar to "Dagger of the Mind" for my liking, although it lacks most of the good qualities of that episode. Most of the fun here is to be had from watching the actors playing the inmates - especially Yvonne Craig as Marta.